1. Field of the Invention
The present invention relates to apparatus for generating electrical power from water flow, and relates particularly, but not exclusively to generating electricity from tidal flow.
2. Description of Related Art
In order to make sources of renewable energy economically viable, the costs of electricity production from renewable energy sources have to be minimised. In particular, in the case of tidal power due to the generally hazardous and aggressive nature of the sea, the costs of production and maintenance of tidal power generation devices are high.
Prior art tidal power generation devices rely on a turbine to align itself with tidal current by rotating around a vertical axis through a mooring point, or by rotating a pillar or other such fixing device. This type of device suffers from the drawback that as a result of the turbine's strong tendency to align itself with the direction of water flow such that the turbine blades rotate about a generally horizontal axis relative to the turbine body (in order to maximise the efficiency of the turbine), movement of the turbine from a forward facing to a rearward facing orientation tends to occur about a generally vertical axis. As a result, repeated rotation of the turbine as a result of changes in the direction of current flow leads to twisting of the mooring cable or any power cable attached to the turbine, which is turn means that complicated and expensive slip ring arrangements become necessary to avoid twisting of the cables, or operation of the power generation apparatus must be halted to enable twisting of the cables to be reversed.